In use the Sigma 17-50mm clearly distinguishes itself as a professional-grade lens in terms of both performance and image quality. It’s an especially easy-to-use lens too – the zoom ring falls within near perfect reach of the thumb and middle finger, with the manual focus ring within easy reach just beyond. The zoom ring is 21mm wide, so there’s plenty to get your fingers around. The zoom action itself is smooth and nicely weighted, with just the right amount of friction. The level of resistance remains constant throughout the entire focal range, so there’s little chance of lens slip should you be pointing your camera upside down at 17mm, or upwards at 50mm.

With our test lens attached to a Nikon D7000 we found focusing near-instantaneous in good to moderate light outdoors, and even indoors under less than ideal artificial light. When light levels drop beyond this, and with our D7000’s AF Assist light switched off, we did encounter some incidence of focus hunting, although this is not unusual.

Manual focusing, however, can be a bit fiddly with barely an inch separating infinity from the Sigma’s minimum focus distance of 28mm. When using a tripod we found it easier to focus using the maximum magnification in live view. Achieving precise focus when shooting hand-held through the viewfinder, can prove a little fiddly though.

Macro capabilities aren’t really the Sigma 17-50mm’s strong point either, although it does offers a minimum focus distance of 28cm throughout its range, with a maximum magnification ratio of 1:5. Sigma also makes a non-stabilised ‘Macro’ version of the 17-50mm f/2.8, so if you are particularly interested in photographing things up close, you may want to take a look at that lens.

Overall we were impressed with the Sigma’s performance. We found the lens to be at its sharpest between f5.6 and f/8 at 27mm, with f/11 also able to produce very sharp results. At these settings the centre is, as might be expected, sharper than the edges, although edge sharpness remains acceptable. All-round performance at 17mm was also very good, although at 50mm we did notice a slight loss of resolution throughout the entire aperture range.

Given that the constant f/2.8 aperture is a big part of the Sigma 17-50mm’s appeal, we were pleased to get good results when using the lens wide open – at least in the centre and borders. Again, we did get slightly better results at 17mm and 28mm than at 50mm, although the difference was pretty marginal. On the flip side, we found resolution tailed off quite quickly beyond f/11 to the minimum aperture setting of f/22. We’re pleased to report that the Sigma performs well in other areas too, helping to produce images with remarkably good levels of contrast and plenty of ‘pop’. Thanks to the FLD elements, chromatic aberrations are very well controlled. That’s not to say they are eliminated altogether, although they are certainly kept to a minimum.

One area where the lens does fall a bit short is barrel distortion, which is fairly pronounced at 17mm. By 24mm things have improved and by 34mm the Sigma is distortion-free. At 50mm a very small amount of pincushion distortion can be seen.

The Sigma 17-50mm is a very good lens that, while not quite perfect, certainly offers a substantial upgrade over a Standard Zoom kit lens. But does it represent good value for money compared to its main rivals? Well, looking at its major-brand competitors both the Canon EF-S 17-55mm f/2.8 IS USM (c.£780) and Nikon 17-55mm f/2.8 ED-IF AF-S DX (c.£1050) are significantly more expensive. The Pentax 16-50mm f/2.8 ED/AL IF (c£610) and Sony DT 16-50mm f/2.8 SSM (£600), meanwhile, are far closer in terms of pricing albeit still slightly more.

Having not tested these lenses individually, we’re not able to compare them directly to the Sigma 17-50mm lens on review here (we hope to get them in at some point in the future of course, at which point we’ll be able to make some direct comparisons). What we can say, with absolute certainty though, is that the Sigma 18-50mm f/2.8 EX DC OS HSM is a very good lens in its own right and, as such, will take some beating.

VerdictWhether you’re buying your first DSLR and want to upgrade the standard zoom kit lens to something a bit more special, or a DSLR owner looking to build a lens collection, the Sigma 17-50mm f/2.8 EX DC OS HSM is a good place to start . While its build quality could be a little tougher and its manual focus ring a little less fiddly, it still has plenty going for it. Capable of good results when used wide open, its constant f/2.8 aperture is as useful as it is creative. Add to this speedy AF performance, built-in optical stabilisation and impressively sharp images from corner to corner at f/5.6-f/11 and it all adds up to a very good package. If you’re looking for a standard zoom upgrade, it’s certainly worth considering.

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